What impressed was how the underdogs showed, particularly Algeria. They had the best opportunities in the first half and exposed a slow German defense that needed goalkeeper Manuel Neuer to play as an auxiliary defender. Neuer came off his line a remarkable 18 times, clearing out plays like an old-style sweeper.

As for Nigeria, talent has never been the question for the most populated country in Africa. Rather, the question marks have typically been organization, teamwork and accountability. They played France well until about the 65th minute, when France began unleashing shot after shot upon Nigerian goalkeeper Vincent Enyeama. By that point, a France goal was almost inevitable, and it came with Enyeama's poor contact on a cross that left France's Paul Pogba an open net for the game-winner.

Monday's World Cup scores

France 2, Nigeria 0

Germany 2, Algeria 1

With higher stakes comes rising caution

Teams scored more goals in the 2014 group stage -- 136 -- than in any prior group stage in World Cup history, and at the highest rate (2.83 goals per game) since 1970.

Now that the knockout stage has started, however, scoring is down to just 13 goals in six games, or 2.2 goals per game. Only three of those goals came before halftime.

The change isn't surprising, though it always disappoints.

Everyone knows that one fatal mistake can send them home, so most teams have played more conservatively. The first halves of this round have often seemed like tactical explorations, as teams feel each other out before making tactical changes at halftime to push for a goal.

There is another factor at play: fatigue. In most leagues around the world, teams play one game a week, typically on the weekend. Midweek games are known to pose significant endurance challenges that lead to backups getting starts. In Brazil, teams are playing every four to five days in a climate hotter than most of them are used to, so it only heightens the impact of fatigue. For example, Algeria tired noticeably late in their loss Monday to Germany, and it probably cost them the game.

Expect more of the same Tuesday. The U.S. will play Belgium in Salvador, located in the northeastern state of Bahia. As a rule, the farther north you go in Brazil, the closer to the Equator you are and the hotter it gets. Meanwhile, Argentina plays Switzerland in Sao Paolo, where the temperature won't be as stifling as the Swiss tendency to focus on defense first, last and always, particularly after their open play against France in the group stage led to a 5-2 blowout loss.

An American referee in Brazil

American referee Mark Geiger has drawn praise during this World Cup for his officiating in two group stage games. As a result, the former high school teacher from New Jersey earned the right to be the first American lead official in a knockout stage game, running the show for Nigeria-France.

As it turns out, he called a loose game, as he often does in Major League Soccer, letting the teams play and stepping in only when necessary. This often draws criticism in MLS, as the American game is much more physical than the styles common in Spain, Chile and Colombia, three of the four teams playing in Geiger's first two World Cup games.

The second was a mistimed tackle by France's Blaise Matuidi on Nigeria's Ogenyi Onazi that appeared to have broken Onazi's ankle. Geiger gave Matuidi a yellow card rather than eject him. It was in fact a brutal tackle, as the GIF below shows, but Matuidi never left his feet to make it. The yellow was justified. Sometimes, guys get hurt in sports.

That said, the controversy probably hurts Geiger's chances of getting another game in charge at the World Cup. Even if he made the right calls, Americans seldom get the benefit of the doubt when it comes to international soccer. Sorry to say, it's just the way it is.

Player of the day: Manuel Neuer, Germany. With his back line exposed, Neuer cleaned up mess after mess much farther away from his net than any goalkeeper wants to be. His play staved off a potential Algeria upset.

U.S. injury news of the day: U.S. striker Jozy Altidore will be available to play for the first time since a hamstring injury knocked him out of his team's first World Cup game after less than 20 minutes. The U.S. will need him Tuesday against Belgium, one of the most talented squads left in the tourney.

Insult of the day (grassroots version): South Korean fans threw yeot candy at their team upon their return home. In South Korea, telling someone to eat yeot is roughly equivalent to telling them to do something rather graphic and anatomically impossible to themselves.

Insult of the day (corporate version): Dutch airline KLM sent Mexican fans off after their team's 2-1 loss to the Netherlands on Sunday with a sombrero and a mustache in this tweet that drew the ire of Mexicans around the world.

Needless to say, it was followed up by an apology and a delete of the tweet, which fortunately has been preserved by others so you can be amused by KLM's potential lack of media savvy.

Non-apology apology of the day: Luis Suarez. The Uruguayan striker issued an apology for biting Italian defender Giorgio Chiellini in the group stage, though he tap-danced around claiming responsibility for doing it intentionally. Suarez faces a four-month suspension, and the incident could scuttle his transfer to Spanish giants Barcelona. Hence, the half-hearted apology, now that Suarez recognizes he bit off more than he can chew.